题目内容：
根据以下材料，回答题
SmokingCanIncreaseDepressiveSymptomsinTeens
Whilesometeenagersmaypuffoncigarettesto"self-medicate”againsttheblues,scientistsattheUniversityofTorontoandtheUniversityofMontrealhavefoundthatsmokingmayactually（1）depressivesymptomsinsometeens.
"Thisobservationalstudyisoneofthefewtoexaminetheperceived（2）benefitsofsmokingamongteens,"saysleadresearcherMichaelChaiton,aresearchassociateattheOntarioTobaccoResearchUnitoftheUniversityofToronto."（3）cigarettesmayappeartohaveself-medicating（4）ortoimprovemood,inthelongtermwefoundthatteenswhostartedtosmokereportedhigherdepressivesymptoms."
Aspartofthestudy,some662highschoolteenagerscompletedupto20questionnaires（5）theiruseofcigarettestoaffectmood.SecondaryschoolswereselectedtoprovideamixofFrenchandEnglishparticipants,urbanandruralschools,andschools（6）inhigh,moderateandlowsocio-economicneighbourhoods.
Participantsweredividedintothree（7）:neversmokers:smokerswhodidnotusecigarettestoself-medicate,improvemoodorphysical（8）;smokerswhousedcigarettestoself-medicate.
Depressivesymptomsweremeasuredusingascalethataskedhowfelttoofiredtodothings:had（9）goingtosleeporstaying（10）;feltunhappy,sad,ordepressed;felthopelessaboutthefuture;feltvexed,antsyortense;andworriedtoomuchaboutthings.
"Smokerswhousedcigarettesasmood（11）hadhigherrisksofelevateddepressivesymptomsthanteenswhohadneversmoked,"saysco-researcherJenniferO'Loughlin,aprofessorattheUniversityofMontrealDepartmentofSocialandPreventiveMedicine."Ourstudyfoundthatteensmokerswhoreportedemotionalbenefitsfromsmokingareathigherriskof（12）depressivesymptoms."
The（13）betweendepressionandsmokingexists（14）amongteensthatusecigarettestofeelbetter."It's（15）toemphasizethatdepressivesymptomscoreswerehigheramongteenagerswhoreportedemotionalbenefitsfromsmokingaftertheybegantosmoke,"saysDr.Chaiton.
回答(1)题 A．examine
B．increase
C．decrease
D．diagnose
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